Can a diagnosis of multiple sclerosis be made without ruling out neuromyelitis optica spectrum disorder ?

Background: The symptoms of multiple sclerosis (MS) can overlap with neuromyelitis optica spectrum disorder (NMOSD). Although testing is available for aquaporin 4 (AQP4) and myelin oligodendrocyte glycoprotein (MOG) antibodies, screening for NMOSD is recommended but not mandatory to establish a diagnosis of MS. Methods and results: We queried 319,994 individuals who filed claims for MS and NMOSD in a Truven Health Analytics (THA) database and had at least one year of uninterrupted health insurance coverage. Of this cohort, 2001 (0.62%) were diagnosed as having NMOSD after an initial diagnosis of MS, based on ICD 9/10 codes. Since THA only offers claims-based data, we initiated an individual patient-based data search at our medical center to screen for potential misdiagnoses. We identified 4/54 (7.4%) NMOSD cases that were initially diagnosed as having MS. Conclusions: The results from our small study have significant implications-symptoms, clinical presentation or classic radiological findings perhaps cannot reliably separate MS from NMOSD. If our study findings can be replicated, guidelines to diagnose MS ought to recommend that NMOSD be excluded first despite typical clinical and radiological findings pointing to MS.